defrag, installing & unreadable memory

Recently I ran a defrag, which locked and shut down the
computer sometime shortly before it completed.

Now, most programs I try and shut down give me an error
message as follows:

"The instruction at "0x76b2ac0e" referenced memory
at "0x76bce06c". The memory could not be "read". Click
on OK to terminate the program".

Also, I cannot load certain programs onto my computer
(McAfee, most importantly), as the installer window comes
up blank and does not work.

HELP!

defrag, installing & unreadable memory